A thalamo-cortical blackboard model for coordinating visual mental routines

Problem. Primates use task-specific attention mechanisms to analyze visual scenes. To select visual targets in complex tasks, mental processes extract, store, and update visual information covertly. Mental routines conceptualize how attention coordinates such processes (Tsotsos&Kruijne, Front Psychol, 2014), while the visual blackboard paradigm proposes how their operations sequentially unfold in visual cortex (Roelfsema&de Lange, Ann Rev Neurosci, 2016). However, a mechanistic neural account, how cortical algorithms, such as the selection and subsequent labeling of perceptual items in visual search-and-trace tasks (Moro et al., J Neurosci, 2010), are implemented, is missing. Method. We propose a neural model that implements visual routines by thalamo-cortical interaction and prefrontal control. While thalamo-cortical interaction performs feature binding, prefrontal signals exert attentional control to steer the thalamo-cortical operational regime and initiate mental operations composing visual routines. Coincident feedforward and feedback signals up-modulate cortical activity forming attentional labels that encode task-relevant information. Such information feeds to higher-order thalamic nuclei that form a low-dimensional visuotopic map of task-relevance. In return, thalamic input to visual cortex gates feedforward-feedback integration restricting attentional labeling to task-relevant items. While the thalamo-cortical system forms a visual blackboard on which mental operations unfold, the prefrontal module biases the cortical module towards features of interest and initiates operations in the thalamic module that signal relevant item locations. A thalamic read-out of routine responses selects saccadic targets. The model implements parts of a perceptual-cognitive control architecture in a neurally plausible fashion. Results. We show through simulations how mental operations unfold over time in cortex and interface via the thalamo-cortical blackboard to coordinate neural search, trace, and selection operations. The model proposes how cortico-cortical processes realize perceptual binding, where higher-order thalamic operations gate such mechanisms through spatially selective gating (Saalman&Kastner, Curr Op Neurobiol, 2009). Low-dimensional control signals from prefrontal cortex coordinate such tasks sequentially.